My experience with CVT transmissions: I have yet to see anybody make one that is bullet proof longterm, and I've been around them all. The theory is great, they are incredibly efficient, but that's pretty much where it ends. They're incredibly expensive to repair, and almost nobody is willing to work on them. Not a good thing if you keep your cars a long time or beyond the warranty period.
I've heard both good and bad about Hummel's service. My only experience with them is on a used car I sold to someone about 6 years ago when I was working at a local new car store. It was a 40k Altima and when the customer went in for their first oil change 3k miles later, they were told that they needed front brakes because they were almost wore out. Of course the customer was really mad at me...until I showed them the repair order where both the pads AND rotors were replaced before we sold it to them. They were the victim of somebody wanting to pad their paycheck since they're paid on commission.
I deal with many, many shops, and all I can say is that generally, the more intermitant the problem, the harder it is to fix. The symptoms may not match what a recall notice says even though it may be the same problem. In the end, it all boils down to how sharp of a tech and service writer you get. And I've been both the winner and loser many times. So when I find one I like, I stick with them.
And for the record, the standard Nissan factory powertrain warranty is 5yr or 60k miles, and has been for many years.